Mixing device and method for controlling the temperature of a fluid flow

ABSTRACT

A mixing device includes a first inlet ( 84 ) and a second inlet ( 86 ) inlet and an outlet ( 80 ). The first inlet ( 84 ) is connected to the outlet ( 80 ) via a first flow connection and the second inlet ( 86 ) is connected to the outlet ( 80 ) via a second flow connection. A circulation pump assembly ( 24; 46 ) includes an electric drive motor ( 30 ), a control device ( 34 ), for controlling the speed of the drive motor ( 30 ), and at least one impeller ( 68; 100 ) driven by the drive motor. The at least one impeller ( 68; 100 ) is positioned in the first flow connection. The flow connections are configured such that at least one hydraulic pressure generated by the impeller ( 68; 100 ) in the first flow connection acts as hydraulic resistance in the second flow connection.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a United States National Phase Application of International Application PCT/EP2018/070969, filed Aug. 2, 2018, and claims the benefit of priority under 35 U.S.C. § 119 of European Application 17 184 777.5, filed Aug. 3, 2017, the entire contents of which are incorporated herein by reference.

TECHNICAL FIELD

The subject-matters of the invention are a mixing device, a heating system with such a mixing device as well as a method for the temperature adjustment of a fluid flow.

TECHNICAL BACKGROUND

Mixers or mixing devices are often used in heating facilities, in order to adjust the temperature of a heating medium or heat transfer medium. Thus for example in floor heating facilities it is common to reduce the feed temperature of the heating medium by way of admixing heating medium from the return. Adjustable mixing valves which are electromotorically driven and change the mixing ratio between hot heating medium and cold heating medium and thus set a desired outlet-side feed temperature are known, in order to be able to adjust and regulate the temperature. Centrifugal pump assemblies are moreover necessary, in order to circulate the fluid heating medium, in particular water, in the individual heating circuits. Usually, in a floor heating facility, at least two centrifugal pump assemblies are provided, one which delivers the heating medium through a floor heating circuit downstream of the described mixing valve, and, in a heating boiler, a further circulation pump assembly which delivers the heating medium which is heated by the heating boiler and in particular also feeds it to the described mixing valve.

The disadvantages of these arrangements are the costs for the individual components and the energy losses which occur in a mixing valve.

SUMMARY

With regard to this problem, it is the object of the invention to provide a less expensive mixing device which has higher energy efficiency.

This object is achieved by a mixing device with the features specified in claim 1, by a heating system with the features specified in claim 14 as well as by a method with the features specified in claim 16. Preferred embodiments are to be derived from the associated dependent claims, the subsequent description as well as the attached figures.

The mixing device according to the invention is particularly envisaged for use in a heating facility or air-conditioning facility. Here, it is to be understood that when hereinafter the term “heating facility” is used, this according to the invention also includes the application in an air-conditioning facility.

The mixing device according to the invention comprises a first and a second inlet, through which fluids to be mixed, in particular a fluid heating medium or heat transfer medium of different temperatures can be fed to the mixing device. The mixing device moreover comprises an outlet, from which the mixed fluid exits. The first inlet is therefore connected to the outlet via a first flow connection and the second inlet to the outlet via a second flow connection. The first and the second flow connection run out in the inside of the mixing device at a mixing point, at which the mixing of the fed fluids is carried out. The mixing device moreover comprises a circulation pump assembly with an electrical drive motor. In particular, the circulation pump assembly is designed as a centrifugal pump assembly. The drive motor is preferably a wet-running electrical drive motor, concerning which the stator and the rotor are separated by a can or a can pot. Particularly preferably, the rotor of the electrical drive motor can be a permanent magnet rotor.

According to the invention, the electrical drive motor comprises a control device for the speed control of the drive motor. I.e. the control device can change the speed of the drive motor and in particular regulate it (control it with a closed loop). For this, the control device can be equipped with a frequency converter. The drive motor drives at least one impeller in the mixing device. This at least one impeller is situated in the first flow connection through the mixing device and thus, when the drive motor rotates, delivers fluid from the first inlet to the outlet of the mixing device. According to the invention, the arrangement of the flow connections in the inside of the mixing device and their design are such that at least one hydraulic pressure which is produced in the first flow connection by the impeller acts as a hydraulic resistance in the second flow connection. The hydraulic pressure in the first flow connection can therefore influence the flow in the second flow connection via the produced hydraulic resistance. In this manner, an influencing of the mixing ratio is possible solely by way of hydraulic means in the mixing device. This has the advantage that one can make do without actuating drives for a special mixing valve, so that as a whole a simpler construction of the mixing device according to the invention is achieved. Moreover, if one can make do without one or more valves for adjusting the mixing ratio, then furthermore the hydraulic resistance of the complete mixing device can be reduced, by which means energy losses in the mixing device can be reduced and minimized.

The first and the second flow connection unify preferably at a run-out point. This run-out point then forms the previously mentioned mixing point. Moreover, the flow connections are preferably designed in a manner such that the hydraulic resistance acts at the run-out point in the form of a counter-pressure. The flow through the second flow path into the run-out point reduces with an increasing counter-pressure, so that the mixing ratio can be changed by way of changing the counter-pressure.

According to a first possible embodiment, the run-out point can lie in the first flow path at the exit side of the impeller. A counter-pressure is therefore produced at this run-out point, at which the second flow path runs out into the first flow path, by way of the speed change of the impeller, wherein the magnitude of the counter-pressure can vary by way of the speed change. A pressure which has been produced by a further impeller or for example by way of a booster pump in a heating system preferably acts in the second flow path. The run-out point preferably lies at the exit side of the impeller in a casing which surrounds the impeller. In the known manner, such a casing can form a spiral which surrounds the impeller or an annular space which surrounds the impeller. In such a casing, the run-out point is preferably situated in the region of the smallest diameter of the spiral or of the annular space, since the smallest counter pressure which is produced by the impeller prevails there at the run-out point, so that a mixing can also be realized given a comparatively low pressure in the second flow path.

According to a further preferred embodiment of the invention, the at least one impeller comprises a first flow path which is part of the first flow connection. Fluid is then delivered through the first flow connection by way of the impeller via this first flow path. The impeller moreover preferably comprises a second flow path which is part of the second flow connection I.e. when the impeller rotates, it delivers fluid through the second flow connection via the second flow path. Moreover, the flow paths are preferably designed in a manner such that a hydraulic pressure which is produced in the first flow path acts as a hydraulic resistance in the second flow path and/or that a hydraulic pressure which is produced in the second flow path acts as a hydraulic resistance in the first flow path. It is therefore by way of the hydraulic pressure in one of the flow paths that the flow in the other flow path can be influenced via the produced hydraulic resistance in this other flow path. This can either be effected in the manner such that a hydraulic pressure in the first flow path acts as a hydraulic resistance in the second flow path or that a reciprocal influencing of the two flow paths is possible. Thus in particular, the mixing device can be designed such that in a first operating condition, the pressure in the first flow path effects a hydraulic resistance in the second flow path, whereas in the second operating condition, the hydraulic pressure in the second flow path effects a hydraulic resistance in the first flow path. Here, the operating conditions in particular are dependent on the speed of the impeller.

The mixing device is preferably designed such that a hydraulic resistance in one of the flow paths and preferably hydraulic resistances in both flow paths can be changed by way of a speed change of the impeller, so that the flow rate through the flow paths can be influenced, by which means again a mixing ratio between the flows through the two flow paths can be changed. A mixing ratio can therefore be changed by way of the speed change of the impeller or of the drive motor.

According to a preferred embodiment of the invention, the circulation pump assembly in the mixing device comprises two impellers which are arranged to one another in a rotationally fixed manner and which are commonly driven by the drive motor, wherein a first flow path which is part of the first flow connection is formed in a first impeller and a second flow path which is part of the second flow connection is formed in a second impeller. The two impellers can be designed as one piece, so that they are designed in the form of an impeller with two blade arrangements or blade rings which are separated from one another. However, it is also possible for the two impellers to be designed as two separate components and to merely be connected to one another in a rotationally fixed manner.

If the two impellers rotate together, then a delivery and pressure increase each take place via and over the first flow path as well as via and over the second flow path, so that fluid is delivered through the first flow connection as well as through the second flow connection and undergoes a pressure increase in each case.

The first and the second flow path in the at least one impeller or in the two impellers which are connected to one another in a rotationally fixed manner are further preferably designed such that on rotation of the at least one impeller or of the two impellers which are connected to one another in a rotationally fixed manner, they effect pressure developments which are different from one another and in particular different speed-dependent pressure developments. This permits the pressure ratio between the two flow paths to be changed by way of a speed change of the impeller or of the impellers, so that the mutual influencing via the produced hydraulic resistances is changed and a mixing ratio of the flows through the two flow connections can therefore be changed.

According to a further possible embodiment, the outlet sides of the first and second flow path are distanced differently far from the rotation axis of the at least impeller in the radial direction. Given an equal speed, different pressure increases as well as speed-dependent pressure courses can be realized in the two flow paths in this manner.

According to a further preferred embodiment of the invention, the first flow path in the at least one impeller runs from a first suction port to the outer periphery of the impeller and the second flow path extends from at least one second inlet opening of the impeller to the outer periphery of the impeller. Here, the at least one second inlet opening preferably lies radially between the first suction port and the outer periphery of the impeller. On rotation of the impeller, this therefore sucks fluid through the suction port and through the second inlet openings. If the fluid is already fed at a suitable preliminary pressure, then an injection of the fluid into the second inlet openings can occur due to the increased preliminary pressure. Different pressure increases or pressure courses can be achieved given the same speed and further preferably different speed-dependent pressure courses for the first and the second path, by way of the radial distancing of the second inlet opening from the suction port, said pressure courses permitting the change of the hydraulic resistance in at least one of the flow connections or flow paths by way of speed change, in order to thus change a mixing ratio. Moreover, it is possible for a flow through the second flow path to be mixed at the second inlet opening with a flow from the first flow path after an already effected pressure increase of the flow on the first flow path. The fluid in the first flow path for example can firstly be increased to a pressure which corresponds essentially to the pressure of the fluid which is fed at the second inlet opening.

Further preferably, the at least one second inlet opening runs out into at least one flow channel which runs between the first suction port and the outer periphery and which forms at least one section of the first flow path. With regard to this design, a section of the flow channel which is situated downstream of the second inlet opening therefore forms a common flow path which is at least a part of the first as well as part of the second flow path. I.e. the fluid through the first and the second flow path flows through a common flow channel of the impeller preferably downstream of the second inlet opening, in which common flow channel a common pressure increase then takes place on rotation of the impeller. A section of the flow channel which is situated upstream of the second inlet opening is thereby assigned purely to the first flow path, so that a pressure increase only of the fluid which flows through the first flow path is effected in this first section of the flow channel. A mixing of the flows through the first flow path and through the second flow path is then effected in the region of the second inlet opening depending on the pressure of this fluid in the region of the at least one second inlet opening and on the pressure of the fluid which is fed at the second inlet opening. This mixing ratio can be changed by way of changing the pressure ratio and thus the hydraulic resistance.

Further preferably, the at least one impeller comprises a first arrangement of impeller blades, between which first flow channels forming at least a part of the first flow path are situated, and a second arrangement of impeller blades, between which second flow channels forming at least a part of the second flow path are situated. Here, the first arrangement of impeller blades and the second arrangement of impeller blades are preferably situated in two planes which are offset in the direction of the rotation axis of the impeller. Such an arrangement practically forms two impellers which are connected to one another in a rotationally fixed manner, wherein the one impeller is formed by the first arrangement of impeller blades and the other impeller is formed by the second arrangement of impeller blades.

The first arrangement of impeller blades preferably has a different outer diameter than the second arrangement of impeller blades. A different pressure increase and in particular a different pressure course can therefore be achieved in dependence on the speed of the impeller. The hydraulic resistance in at least one of the flow connections, for example in the two flow channels between the impeller blades of the second arrangement of impeller blades can therefore be changed in a speed-dependent manner. As described above, the flow rate through these flow channels can thus be varied depending on the produced hydraulic resistance.

According to a further preferred embodiment of the invention, the first arrangement of impeller blades is connected to the first suction port of the impeller and the second arrangement of impeller blades is connected to a second suction port which forms a second inlet opening of the impeller. This second suction port surrounds the first suction port preferably in an annular manner. As an alternative, the second suction port could also be arranged away from the first suction port in the axial direction, so that the inflow directions into the impeller through the two suction ports are directed axially opposite one another. This arrangement would have the advantage that the occurring axial forces at least partly cancel one another out. The annular or concentric arrangement of the first and of the second suction port has the advantage that such a design can be integrated relatively simply into a known pump casing.

According to a further preferred embodiment of the invention, the control device is designed in a manner such that it varies the speed of the drive motor for regulating a mixing ratio between a fluid flow through the first inlet and a fluid flow through the second inlet. As already described beforehand, given a suitable design of the impeller and of the flow paths or flow connections, the hydraulic resistance in at least the second flow connection changes given a speed change of the drive motor, so that the flow rate in the second flow connection can be varied. The mixing ratio can moreover the changed by way of a speed change of the drive motor, without a mixing valve which is adjustable via a separate actuating drive becoming necessary.

The control device is preferably connected to at least one temperature sensor in the outlet or in a flow path which is situated downstream of the outlet, and/or is designed for receiving a signal from at least one external temperature sensor and is designed in a manner such that it varies the speed of the drive motor in dependence on at least one received temperature signal. I.e., with this design of the control device, a regulation to a desired pressure or flow rate does not take place, but towards a desired temperature. The control device is preferably designed such that it regulates speed of the drive motor such that a temperature value which is detected by the temperature sensor reaches a predefined setpoint or approximates (approaches) a predefined setpoint. This setpoint can be defined of example by a heating curve which is turn sets a feed temperature to be reached at the outlet of the mixing device, for the heating medium, e.g. in a manner depending on the outer temperature.

Apart from the described mixing device, the subject-matter of the invention is a heating system with a mixing device as has been described above. In such a heating system, the first inlet of the mixing device is connected to a return of at least one heating circuit, for example of a floor heating circuit, and the second inlet of the mixing device is connected to a feed which comes from a heat source. Such a heat source for example can be a heating boiler such as a gas or oil heating boiler, a heat store, a solar facility, an electrical heat source, a district heat facility or the like. The heat source heats a fluid heat transfer medium or a fluid heating medium which is to be fed to one or more heating circuits. Due to the fact that the mixing device is arranged upstream of the heating circuit, it is possible to adapt the temperature of the fluid heating medium, in the case of a heating facility to reduce it, by way of heating medium from the return being admixed from the return. With the mixing device according to the invention, it is therefore possible to deliver the fluid heating medium in circulation in the heating circuit with the help of the circulation pump assembly in the mixing device, whilst only as much warmer heating medium as is necessary for the thermal demand of the heating circuit is admixed through the first inlet. Thus for example an injection arrangement, via which the heated heating medium in the mixing device is injected into the flow through the heating circuit can be realized. A corresponding part of the fluid flow is then led out of the heating circuits back again to the heat source, in order to be heated again there.

Particularly preferably, a second circulation pump assembly can be arranged in the feed in a manner such that it provides a fluid, in particular a fluid heat transfer medium or a fluid heating medium at a preliminary pressure at the second inlet of the mixing device. Such a second circulation pump assembly can be for example a circulation pump assembly which is integrated into the heat source, in particular into the heating boiler. This second circulation pump assembly can moreover simultaneously serve for feeding the fluid or the heat transfer medium to a further heating circuit. It is possible to utilize the preliminary pressure, at which the fluid is provided at the second inlet due to the fact that the mixing device, as described above, is designed such that different pressure increases are reached for the two flow paths through the impeller. I.e., the pressure does not have to be relieved in a valve arranged upstream, so that energy losses can be minimized. The preliminary pressure can moreover contribute to the speed-dependent pressure courses through the two described flow paths of the impeller being different to the extent that the hydraulic resistance in at least one of the flow connections and in particular of the second flow connection can be varied by way of speed variation, in order to change the mixing ratio.

Apart from the previously described mixing device and the previously described heating system, the subject-matter of the invention is a method for the temperature adjustment of a fluid flow in a heating facility, as is described hereinafter. A heating facility in the context of the invention is furthermore also to be understood as an air-conditioning facility which serves for cooling the facility or a building. I.e. the heating facility according to the invention can be designed for heating rooms or facilities and/or for cooling rooms or facilities.

According to the inventive method for the temperature adjustment of a fluid flow, two differently temperature-adjusted fluid flows, for example two differently temperature-adjusted heating medium or heat transfer medium flows are mixed in a changeable mixing ratio. According to the invention, this is effected by way of the two differently temperature-adjusted fluid flows being fed to a common mixing point or run-out point, at which a hydraulic resistance acts upon at least one of the two fluid flows. This hydraulic resistance limits the fluid flow, upon which it acts. According to the invention, this hydraulic resistance can be changed by way of hydraulic means for changing the mixing ratio. The hydraulic resistance is thus changed, in order to influence at least one of the two fluid flows, so that the mixing ratio changes. The hydraulic means which change the hydraulic resistance are designed such that they act upon at least one of the two fluid flows. As described above by way of the mixing device, the hydraulic resistance in particular is a fluid pressure or counter-pressure of the other fed fluid flow which acts at the mixing point. The counter-pressure at the mixing point can be varied via the circulation pump assembly by way of a speed change due to different pressure courses of the fluid flows, so that different mixing ratios occur.

Further preferably, the hydraulic resistance is varied by way of changing the fluid pressure of the first and/or the second fluid flow. I.e., at least one of the fluids flows itself forms a hydraulic resistance for the other fluid flow. Particularly preferably, the both fluid flows form reciprocal hydraulic resistances. Hence by way of a pressure change in one of the fluid flows, the hydraulic resistance in the other fluid flow is changed, so that the flow rate of this other flow can be varied, so that different mixing ratios result. A changeable pressure increase in at least one of the two fluid flows is preferably effected by way of pressure increasing/boosting means, wherein the pressure increase is preferably effected by an impeller of a centrifugal pump assembly. This can be effected as was described above by way of the mixing device. The pressure in at least one flow path through the impeller changes by way of speed change of the impeller of the centrifugal pump assembly, so that the pressure in a fluid flow through this flow path can be changed.

According to a particular embodiment of the invention, one of the two fluid flows can already have a higher greater preliminary pressure than the other fluid flow already before the effect of the pressure boosting means. A shifting of the speed-dependent pressure courses can be achieved by way of this, said shift, given a speed change, being able to be utilized in order to vary the pressure ratio of the two fluid flows to one another and to thereby change at least the hydraulic resistance to one of the fluid flows, in order to adjust the mixing ratio.

Regarding further details of the method according to the invention, the aforesaid description of the function of the mixing device and of the heating system is referred to. The features which are described there are likewise preferred subject-matters of the method according to the invention.

The invention is hereinafter described by way of example and by way of the attached figures. The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this disclosure. For a better understanding of the invention, its operating advantages and specific objects attained by its uses, reference is made to the accompanying drawings and descriptive matter in which preferred embodiments of the invention are illustrated.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a hydraulic circuit diagram of a heating facility according to the state of the art;

FIG. 2 is a hydraulic circuit diagram of heating system according to a first embodiment of the invention;

FIG. 3 is a hydraulic circuit diagram of a heating facility according to a second embodiment of the invention;

FIG. 4 is a hydraulic circuit diagram of a heating system according to a third embodiment of the invention;

FIG. 5 is a hydraulic circuit diagram of a heating facility according to the embodiment example according to FIG. 3, with a double impeller;

FIG. 6 is an exploded perspective view of a circulation pump assembly with a mixing device according to the heating system according to FIGS. 2, 3, and 5;

FIG. 7 is a sectional view of the circulation pump assembly according to FIG. 6 along its longitudinal axis X;

FIG. 8 is a plan view of the rear side of the circulation pump assembly according to FIGS. 6 and 7;

FIG. 9 is a partly sectional view of the rear side of the circulation pump assembly according to FIGS. 6 to 8;

FIG. 10 is an exploded perspective view of a circulation pump assembly with a mixing device according to the embodiment example according to FIG. 4;

FIG. 11 is a sectional view of the circulation pump assembly according to FIG. 10, along longitudinal axis X;

FIG. 12 is a plan view of the rear side of the circulation pump assembly according to FIGS. 9 and 10;

FIG. 13 is a graph of the pressure course over the speed for the embodiment example of a heating system according to FIG. 2;

FIG. 14 is a graph of the pressure course over the speed for an embodiment example of a heating system according to FIG. 3; and

FIG. 15 is a graph of the pressure course over the speed for an embodiment example of a heating system according to FIG. 4.

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring to the drawings, FIG. 1 schematically shows a conventional heating circuit for a floor heating 2, i.e. a heating circuit according to the state of the art. A heating boiler 4, for example a gas heating boiler with an integrated circulation pump 6 serves as a heat source. Such combinations are known on the market as compact heating facilities. A further circulation pump assembly 8 with an impeller 10 as well as with an electrical drive motor 12 is provided for the floor heating circuit 2. Here, a mixing device is provided since the heating boiler 4 has too high a feed temperature for the floor heating 2, wherein this mixing device has a mixing point 14 which is situated at the suction side of the impeller 10. A return conduit 16 of the floor heating circuit 2 runs out at the mixing point 14. A feed conduit 18, via which the water or heating medium which is heated by the boiler 4 is fed and injected at the mixing point 14 by the pressure produced by the circulation pump assembly 6 runs out at the mixing point or run-out point 14. In this example, two flow regulation valves R_(hot) and R_(cold) are provided for regulating the mixing ratio. The regulating valve R_(hot) is arranged in the feed conduit 18 and the regulating valve R_(cold) in the return conduit 16. The valves can be activated for example by a control device via an electrical drive. The regulating valves R_(hot) and R_(cold) can preferably be coupled such that one of the valves is always opened and the other valve is simultaneously closed by the same amount, for changing the flow rate. A 3-way valve which comprises a valve element which by way of its movement simultaneously closes the return conduit 16 and opens the feed conduit 18 or vice versa can also be used instead of two flow regulation valves R. The circulation pump assembly 6 can moreover supply a further heating circuit which is not shown here and which is operated directly with the feed temperature produced by the heating boiler. The circulation pump assembly 6 as well as the circulation pump assembly 8 can have a conventional pressure regulation or flow-rate regulation. Concerning the known system, it is a disadvantage that the flow regulation valves R are necessary for adjusting the mixing ratio and need to be provided with a suitable drive, for example with a motorically or thermostatically actuated drive. The flow regulation valves R are regulated such that a desired feed temperature for the flow heating 2 is reached downstream of the mixing point 14. A further disadvantage in this system is the fact that the pressure which is produced by the circulation pump assembly 6 needs to be reduced via the flow regulation valve R_(hot) in order to achieve the suction-side pressure of the impeller 10 at the mixing point 14. An energy loss thus occurs in the system, and this loss can be avoided with the solution according to the invention which is described hereinafter.

Concerning the three solutions according to the invention which are described by way of example and are schematically represented in FIGS. 2 to 4, the mixing ratio for achieving a desired feed temperature for the floor heating 2 is achieved solely by way of a speed regulation of a circulation pump assembly. This assembly comprises two flow paths which mutually hydraulically influence one another such that the hydraulic resistance in at least one of the flow paths can be changed by way of a speed change, in order to change the mixing ratio as is described hereinafter.

FIG. 2 shows a first embodiment example of the invention. In this, again a heating boiler 4 is provided for heating a fluid heating medium, i.e. a fluid heat-transfer medium such as water. A circulation pump assembly 6 is moreover arranged on this boiler 4 and could also be integrated into the heating boiler 4, as has been explained regarding FIG. 1. The circulation pump assembly 6 delivers heat transfer medium in a feed conduit 18. A floor heating 2 or a floor heating circuit 2 is moreover provided and this comprises a return which on the one hand is connected to the inlet side of the heating boiler 4 and on the other hand leads via a return conduit 16 to a mixing point 20, at which the feed conduit 18 also runs out. The mixing point or run-out point 20 is part of a mixing device 22 and moreover of a circulation pump assembly 24. The mixing device 22 and the circulation pump assembly 24 can form an integrated construction unit, so that the mixing device 22 is part of the circulation pump assembly 24 or the circulation pump assembly 24 is part of the mixing device. In particular, the mixing point 20 can lie directly in the pump casing or in an impeller of the circulation pump assembly 24, as is described hereinafter.

In the embodiment example according to FIG. 2, the circulation pump assembly 24 is designed as a double pump with two impellers 26 and 28. The impellers 26 and 28 are driven via a common drive motor 30. The impellers 26 and 28 can be designed as separate impellers or as an integrated impeller with two blade arrangements or flow paths. The first impeller 26 forms a first flow path and lies in a first flow connection in the mixing device from the return conduit 16 to the mixing point 20. The second impeller 28 forms a second flow path and lies in a second flow connection between the feed conduit 18 and the mixing point 20. The mixing point 20 therefore lies at the delivery side of the two impellers 26 and 28, i.e. according to the invention, the two heating medium flows are mixed with one another after a pressure increase.

The drive motor 30 is controlled or regulated by a control device 34 which serves for speed regulation or speed control of the drive motor 30 and is designed such that it can change the speed of the drive motor 30. For this, the control device 34 comprises a speed controller, in particular amid the application of a frequency converter. The control device 34 can be integrated directly into the drive motor 30 or be arranged in an electronics casing directly on the drive motor and in particular on the motor casing of this motor. The control device 34 is moreover connected to a temperature sensor 36 or communicates with a temperature sensor 36. The temperature sensor 36 is situated downstream of the mixing point 20 on or in the feed conduit 38 which connects the mixing point 20 to the floor heating circuit 2. Here, the temperature sensor 36 can be integrated into the mixing device 22 or into the circulation pump assembly 24. The connection of the temperatures sensor 36 to the control device 34 can be provided in an arbitrary manner, for example connected by wire or also in a wireless manner. A wireless connection can be realized for example via a radio connection such as Bluetooth or W-LAN.

The temperature sensor 36 transmits a temperature value of the heating medium downstream of the mixing point 20 to the control device 34, so that this can carry out a temperature regulation. According to the invention, the drive motor 30 and therefore the circulation pump assembly 34 is not regulated in a pressure-dependent or flow-rate-dependent manner, but in a temperature-dependent manner. I.e. the control device 34 adapts the speed of the drive motor 30 such that a desired temperature of the heating medium is reached downstream of the mixing point 20. The desired temperature is defined by a temperature setpoint which can be set in a fixed manner, can be manually adjusted or can be specified depending on the outer temperature by a heating curve which is stored in the control device 34 or a superordinate control. The control device 34 varies the speed of the drive motor 30, by which means, as described hereinafter, the mixing ratio of the heating medium flows which are mixed at the mixing point 20 changes, so that the temperature downstream of the mixing point 20 changes. This temperature is detected by the temperature sensor 36, so that the control device 34 can carry out a temperature regulation by way of speed variation of the drive motor 30, in order for the temperature value downstream of the mixing point 20 to approximate the temperature setpoint.

The variation of the mixing ratio at the mixing point 20 via the speed change is explained in more detail by way of FIG. 13. In FIG. 13, the delivery head H, i.e. the pressure is plotted against the speed n of the drive motor 30. In the example which is shown in FIG. 2, there are three differential pressure values ΔP_(pre), ΔP_(hot) and ΔP_(cold). The differential pressure ΔP_(pre) is produced by the circulation pump assembly 6 and in this case cannot be influenced by the mixing device 22, so that it is represented in FIG. 13 as a constant preliminary pressure, i.e. one which is independent of the speed of the drive motor 30. The impeller 26 of the circulation pump assembly 24 produces a differential pressure ΔP_(cold) for the return of the floor heating 2 and the impeller 28 produces a differential pressure ΔP_(hot) for the feed from the feed conduit 18. As is to be recognized in FIG. 13, the impellers 26 and 28 are designed differently, so that they have different pressure courses, i.e. different speed-dependent pressure courses. The pressure course for the impeller 28 is less steep than the pressure course of the impeller 26. This can be achieved for example by way of the impeller 26 having a larger outer diameter. The differential pressures ΔP_(pre) and ΔP_(hot) moreover sum for the heated heating medium which is fed through the feed conduit 18, so that the curve of the pressure course ΔP_(hot) is shifted to the top in the diagram by a constant value. One succeeds in the pressure course curves ΔP_(hot) and ΔP_(cold) intersecting at a point 39 by way of this. Mixing regions 40 for the mixed fluid result above and below the intersection point of these curves. Given a speed n below the intersection point 39 of the two pressure course curves, the outlet pressure of the impeller 28 is higher than that of the impeller 26, so that the outlet pressure of the impeller 28 in the flow path through the impeller 26 acts at the mixing point 20 as a counter-pressure and a hydraulic resistance and in this operating condition the flow rate through the first flow path through the impeller 26 is reduced and more heated heating medium is admixed, in order to reach a higher temperature in the feed 38 to the floor heating circuit 2. If the speed is increased, then the outlet pressure of the impeller 26 is greater than that of the impeller 28 above the intersection point 39 of the two pressure course curves, so that a hydraulic resistance in the form of a counter-pressure is produced at the mixing point 20 in the second flow path through the impeller 28 and the flow rate through the second flow path is reduced, by which means less heated heating medium is fed at the mixing point 20 and the temperature at the outlet side of the mixing point 20 can be reduced.

FIG. 3 shows a further variant of a mixing device according to the invention or of a heating system according to the invention, which differs from the heating system according to FIG. 2 in that no circulation pump assembly 6 is provided in the feed 18. I.e. the heated heating medium is fed to the circulation pump assembly 24 via the feed conduit 18 without a preliminary pressure. The curves of the pressure course which are shown in FIG. 14 result on account of this. Again, in FIG. 14 the delivery head H, i.e. the pressure is plotted against the speed n of the drive motor 30. The pressure course curves ΔP_(cold) and ΔP_(hot) correspond to the pressure course curves which are shown in FIG. 13. It is only the constant preliminary pressure ΔP_(pre) which is absent, so that the pressure course curve ΔP_(hot) is not shifted upwards in the diagram, but begins at the origin just as the pressure course curve ΔP_(cold). However, both curves have a different gradient which again, as described above, is achieved by a different impeller diameter of the impellers 26 and 28. The hydraulic resistances change due to the fact that the differential pressure at the impellers 26 and 28 changes to a different extent given a change in speed, by which means a mixing region 42 results between the two pressure course curves with a resulting differential pressure. The higher outlet pressure ΔP_(cold) of the impeller 26 acts as a hydraulic resistance in the second flow path through the impeller 28 at the mixing point 20. The hydraulic resistance results from the pressure difference between the outlet pressures of the impellers 26 and 28 at the mixing point 20. As can be recognized in FIG. 14, this pressure difference between the pressure course curves ΔP_(cold) and ΔP_(hot) (the mixing region 42) is speed-dependent. I.e. the hydraulic resistance which acts in the flow path through the impeller 28 can thus also be varied by way of speed change, so that the flow rate through the impeller 28 and thus the flow rate of heated heating medium can be changed. A change of the temperature at the outlet side of the mixing point 20 and, with this, a temperature regulation is therefore also possible by way of a speed change of the speed n of the drive motor 30.

FIG. 5 shows an embodiment example which represents one variant of the embodiment example which is shown in FIG. 2. The two impellers 26 and 28 are designed in the form of a double impeller. I.e. the impeller 26 is formed by a first blade ring and the impeller 28 by a second blade ring of the same impeller. The variation of the mixing ratio at the mixing point 20 via a change of the speed n of the drive motor 30 is effected in the same manner as described by way of FIGS. 3 and 13. In this embodiment example, a flow regulation valve R_(hot) is additionally provided in the feed conduit 18 and as well as a flow regulation valve R_(cold) in the return conduit 16, upstream of the impellers 26 and 28. These are manually adjustable valves, with which a presetting can be carried out before the described speed regulation control is carried out. The presetting is preferably effected in a manner such that the speed of the drive motor 30 is firstly set such that an adequate flow rate through the floor circuit 2 is achieved. I.e. the speed of the impellers 26 and 28 is firstly set such that a differential pressure which is matched to the facility, i.e. to the hydraulic resistance of the facility, is produced. The manual flow regulation valves R_(hot) and R_(cold) are subsequently adjusted or set such that a desired temperature setpoint is reached at the temperature sensor 36 at the given speed. This temperature setpoint for example can be a temperature setpoint which is set by a heating curve given the current outer temperature. A compensation between the different hydraulic resistances in the feed conduit 18 and the return conduit 16 is achieved by the manual presetting. After this presetting, the temperature regulation can then be carried out by way of speed regulation with the help of the control device 34, wherein only slight speed changes are necessary for temperature adaptation, as results from the diagram in FIG. 13. Such valves for presetting can also be used with the other described embodiments examples.

FIG. 4 shows a third variant of a heating system with a mixing device according to the invention. A heating boiler 4 with a circulation pump assembly 6 which is arranged downstream is also provided in this heating system. A floor heating 2 or a floor heating circuit 2 which is to be supplied is also provided. Here too, a mixing device 44 is present, in which mixing device a heating medium flow from a feed 18 which extends in a manner departing from the heating boiler 4 is mixed with a heating medium flow from a return conduit 16 from the return of the floor heating 2. In this embodiment example, the mixing device 44 again comprises a circulation pump assembly 46 with an electrical drive motor 30. This drive motor 30 is also regulated in its speed by the control device 34 which can be integrated directly into the drive motor 30 or in an electronics casing directly on the drive motor 30. As with the preceding embodiment examples, the control device 34 is communicatingly connected to a temperature sensor 36 which is situated on a feed conduit 38 to the floor heating circuit 2, so that it detects the feed temperature of the heating medium which is fed to the floor heating circuit 2. A temperature-dependent speed control can therefore also be carried out with regard to the circulation pump assembly 36 in the manner described above.

The embodiment example according to FIG. 4 differs from the previously described embodiment examples in that the circulation pump assembly although comprising no impellers arranged in parallel however comprises impeller parts 48 and 50 which are arranged in series. The impeller parts 48 and 50 can be designed as two separate impellers which are connected to one another in a rotationally fixed manner, so that these are rotatingly driven via the common drive motor 30. Particularly preferably, the impeller parts 48, 50 are however designed as an impeller which between a first central inlet opening and the outlet opening comprises at least one second inlet openings in a radially middle region, as described in more detail below. Concerning this embodiment example, this second inlet opening forms the mixing point or run-out point 52, at which the two fluid flows or heating medium flows from the return conduit 16 and the feed conduit 18 are mixed. The heating medium flow from the return conduit 16 undergoes a first pressure increase ΔP₁ upstream of the mixing point 52 via the impeller part 48. The heating medium flow from the feed conduit 18 undergoes a pressure increase ΔP_(pre) by way of the circulation pump assembly 6. At the run-out point 52, the heating medium flow is injected at this preliminary pressure into the heating medium flow which leaves the impeller part 48. The run-out point 52 and the second impeller part 50 form a second flow path. The heating medium flow from the feed conduit 18 and, in the further course downstream of the run-out point 52, also the heating medium flow which is from the return conduit 16 and which has previously undergone a pressure increase in a first flow path in the impeller part 48, flow through this second flow path. The mixed heating medium flow undergoes a further pressure increase ΔP₂ in the impeller part 50.

With this configuration too, the mixing ratio between the heating medium flow from the return conduit 16 and the heating medium flow from the feed conduit 18 can be changed by way of a speed change, as is described in more detail by way of FIG. 15. In FIG. 15, the pressure courses in the form of the delivery head H are again plotted against the speed n of the drive motor 30. The constant preliminary pressure ΔP_(pre) which is produced by the circulation pump assembly 6 is to be recognized as a horizontal line in the diagram in FIG. 15. Moreover, the two speed-dependent pressure courses ΔP₁ and ΔP₂ are again shown. Here, the pressure course ΔP₂ has a steeper course than the pressure course ΔP₁, i.e. given an increase of the speed, the pressure ΔP₂ rises more rapidly than the pressure ΔP₁. A mixing region 54, in which different mixing ratios can be realized is located between the pressure course ΔP₁ and the preliminary pressure ΔP_(pre). The hydraulic resistance in the second flow path to the impeller part 50 increases at the mixing point 52 with an increasing pressure ΔP₁ which the heating medium flow from the return conduit 16 undergoes in the impeller part 48. A counter-pressure forms at the mixing point 52 and this counter-pressure serves as a hydraulic resistance for the heating medium flow which enters into the mixing point 52 from the feed conduit 18. The higher the counter-pressure at the mixing point 52, the lower becomes the flow rate through this second flow path through the run-out point, i.e. the smaller does the heating medium flow which enters from the feed conduit 18 into the mixing point 52 and thus into the second flow path become. The warm water flow, i.e. the heating medium flow from the feed conduit 18 is completely disconnected when the preliminary pressure ΔP_(pre) is exceeded by the pressure ΔP₁. The mixing ratio can therefore be changed by way of speed change. The mixed heating medium flow then undergoes the pressure increase to the pressure ΔP₂ in the second impeller part 50.

This arrangement has the advantage that the pressure ΔP_(pre) which is produced by the circulation pump assembly 6 does not have to be reduced, since the mixing of the two heating medium flows takes place at a greater pressure level, specifically at the level of the pressure ΔP₁. Energy losses in the mixing device 44 are reduced by way of this. In a further alternative embodiment of the invention, one can make do without the impeller 50 which is situated downstream of the run-out point or mixing point 52, or the impeller part 50 which is situated there, if a further pressure increase is not desired at the mixing point or downstream of this mixing point. This for example could be an application case, in which the pressure increase ΔP_(pre) and ΔP₁ is adequate for the operation of the floor heat circuit. The pressure ΔP₁ can be varied by way of changing the speed of the impeller or the impeller part 48, by which means the counter-pressure at the mixing point 52 is varied for the fluid which is fed through the feed conduit 18 and hence the mixing ratio is changed. The mixing point 52 is preferably situated in the exit region of the impeller part or of the impeller 48 at a small as possible diameter in a region of small as possible pressure, so that a low as possible preliminary pressure is sufficient for injecting the fluid at the mixing point 52.

The design construction of the mixing devices 22 and 44 are hereinafter described in more detail by way of the FIGS. 6 to 12. Here, FIGS. 6 to 9 show a mixing device which is used as a mixing device 22 in the embodiment examples according to FIGS. 2, 3 and 5. FIGS. 10 to 12 show a mixing device 44 as is applied with the embodiment example according to FIG. 4.

The embodiment example according to FIGS. 6 to 9 shows an integrated circulation pump mixing device, i.e. a circulation pump assembly with an integrated mixing device or a mixing device with an integrated circulation pump assembly. The circulation pump assembly in the known manner comprises an electrical drive motor 30, on which an electronics casing or terminal box 56 is attached. In this embodiment example, the control device 34 is arranged in the electronics casing. The electrical drive motor comprises a stator or motor casing 58, in whose interior the stator 60 of the drive motor 30 is arranged. The stator 60 surround a can pot or can 62 which separates the stator space from a centrally situated rotor space. The rotor 64 which can be designed for example as a permanent magnet rotor is arranged in the rotor space. The rotor 64 is connected to the impeller 68 via a rotor shaft 66, so that the rotor 64, given its rotation about the rotation axis X, rotatingly drives the impeller 68.

In this embodiment example, the impeller 68 is designed as a double impeller and unifies the impellers 26 and 28, as has been described by way of FIGS. 2 and 5. The impeller 68 comprises a central suction port 70 which runs out into a first blade arrangement or into a first blade ring which forms the impeller 26. A first flow path through the impeller 68 is therefore defined by the suction port 70 and the impeller 26. The impeller 26 is designed in a closed manner and comprises a front shroud 72 which merges into a collar which delimits the suction port 70. A second blade ring which forms the second impeller 28 is arranged or formed on the front shroud 72. The second impeller 28 at the inlet side comprises an annular suction port 74 which annularly surrounds the suction port 70. The second suction port 74 forms a second inlet opening of the impeller 68. Departing from the second suction port 74, the impeller 28 forms a second flow path through the impeller 68. The impeller 26 as well as the impeller 28 comprises outlet openings at the peripheral side, said outlet openings running out into a delivery chamber 76 of a pump casing 78.

The pump casing 78 is connected to the motor casing 58 in the usual manner. The delivery chamber 76 in the inside of the pump casing 78 runs out into delivery pipe connection 80, onto which the feed conduit 38 to the floor heating circuit 2 would connect in the embodiment examples according to FIGS. 2, 3 and 5. Since both impellers 26 and 28 run out into the delivery chamber 76, the mixing point 20 which is described by way of FIGS. 2, 3 and 5 lies at the outlet side of the impeller 68 in the delivery chamber 76 of the pump casing 78.

The first suction port 70 of the impeller 68, in the pump casing 78 is in connection with a first suction conduit 82 which begins at a first suction pipe connection 84. This first suction pipe connection 84 lies in a manner in which it is axially aligned to the delivery pipe connection 80 along an installation axis which extends normally to the rotation axis X. In the embodiment examples according to FIGS. 2, 3, and 5, the return conduit 16 is connected to the suction pipe connection 84. In this embodiment example, a flow regulation valve R_(cold) as is shown in FIG. 5 is moreover arranged in the suction conduit 82.

A first flow connection through the pump casing 78 is defined from the suction pipe connection 84 which forms a first inlet, via the suction conduit 82, the suction port 70, the first impeller 26, the delivery chamber 76 and the delivery pipe connection 70. The pump casing 78 moreover comprises a second suction pipe connection 86 which forms a second inlet. In the inside of the pump casing 78, the second suction pipe connection is connected to an annular space 90 at the suction side of the impeller 68 via a connection channel 88. The annular space 90 surrounds a ring element 92 at the outer periphery. The ring element 92 is inserted into the suction chamber of the pump casing 78 and with its annular collar is in engagement with the collar which surrounds the suction port 70, so that a sealed flow connection is created from the suction channel 82 into the suction port 70. The ring element 92 is surrounded by the annular space 90 at the outer periphery, so that the ring element 92 separates the flow path to the suction port 70 from the flow path to the second suction port 74. An annular sealing element 94 which bears on the inner periphery of the pump casing 78 and comes into sealing bearing contact with the outer periphery of the impeller 68 is inserted into the pump casing. Here, the sealing element 94 is in sealing bearing contact with the impeller 68 in the outer peripheral region of the second suction port 74, so that in the pump casing 76 it separates the suction region from the delivery chamber at the inlet side of the suction port 74.

A check valve 96 which prevents a backflow of fluid into the feed conduit 18 is moreover arranged in the flow path from the second suction pipe connection 86 to the connection channel 88. The feed conduit 18, as is shown in FIGS. 2, 3 and 5, is connected onto the second suction pipe connection 86.

A temperature adjustment of the heating medium which is fed to the floor heating circuit 2 can be achieved with the shown circulation pump assembly 24 with the integrated mixing device 22 by way of a speed change of the drive motor 30, as was described by way of FIGS. 2, 3 and 5 as well as 13 and 14.

A presetting can be carried out via the flow regulation valves R_(cold) and R_(hot) as described by way of FIG. 5. In this embodiment example, the flow regulation valves R_(cold) and R_(hot) are designed as rotatable valve elements 98 which are each inserted into a cylindrical receiving space. The valve elements 98 get into the suction conduit 82 to a different extent or cover the connection channel 88, by way of rotation, so that the free flow cross section in the first or second flow path can be changed by way of rotating the respective valve element 98.

FIGS. 10 to 12 show an embodiment example of the circulation pump assembly 46 with the mixing device 44 as has been described by way of FIGS. 4 and 15. Here too, the mixing device 44 and the circulation pump assembly 46 represent an integrated construction unit. The drive motor 30 with the attached electronics casing 56 with regard to one construction corresponds to the drive motor 30 as has been described by way of FIGS. 7 to 9. The pump casing 78′ with regard to its construction also corresponds essentially to the previously described pump casing 78. A first difference lies in the fact that the pump casing 78′ has no flow regulation valves R_(hot) and R_(cold), wherein it is to be understood that such flow regulation valves R as have been described beforehand could also be provided in this second embodiment example. A second difference lies in the fact that the second suction pipe connection 86′ in this embodiment example has an outer thread. However, it is to be understood that the suction pipe connection 86 according to the preceding embodiment example could also be designed accordingly or the suction pipe connection 86′ could likewise comprise an inner thread.

In the second embodiment example, an impeller 100 is connected to the rotor shaft 66. This impeller 100 comprises a central suction port 102 whose peripheral edge is sealingly engaged with the ring element 92, so that a flow connection is created from the first suction pipe connection 84 into the impeller 100. The impeller 100 comprises only one blade ring which defines a first flow path departing from the suction port 102 which forms a first inlet opening, to the outer periphery of the impeller 100. This first flow path runs out into the delivery chamber 76 which is connected to the delivery pipe connection 80. An annular space 90, into which the connection channel 88 runs out from the second suction pipe connection 86 is again present surrounding the ring element 92. The impeller 100 comprises front shroud 104. Openings 106 which form second inlet openings are formed in this shroud. These openings 106 run out into the flow channels 108 between the impeller blades. Here, the openings 106, seen radially with respect to the rotation axis X, run out into the flow channels 108 in a region between the suction port 102 and the outer periphery of the impeller 100. I.e. the openings 106 run out into a radial middle region of the first flow path through the impeller 100. The openings 106 and the flow channels 108 with their sections radially outside the openings 106 form second flow paths which correspond to the impeller part 50 as has been described by way of FIG. 4. The impeller part 78 is formed by the radially inwardly lying impeller part, i.e. in the flow direction between the suction port 102 and the openings 106. The openings 106 face the annular space 90 so that heating medium can enter these openings 106 via the connection channel 88. In this embodiment example, the mixing point 52 according to FIG. 4 therefore lies in the flow channels 106 at the outlet side of the opening 106.

The impeller 100 on its outer periphery, i.e. on the outer periphery of the shroud 104 comprises an axially directed collar 110 which bears on the inner periphery of the pump casing 78′ and therefore seals the annular space 90 with respect to the delivery chamber 76. A temperature regulation of the heating medium flow which is fed to the floor heating circuit 2 can be carried out as is described by way of FIGS. 4 and 15, with the circulation pump assembly 46 with an integrated mixing device 44 which is shown in FIGS. 10 to 12.

Concerning the three solutions according to the invention which are described by way of example, a regulation of the temperature has been described by way of adjusting the mixing ratio solely by way of speed change. However, it is to be understood that such a feed temperature regulation could also be realized in combination with an additional valve R_(hot) in the feed conduit 18 and/or a valve R_(cold) in the return conduit 16. Here, the valves R_(hot) and R_(cold) can possibly be coupled to one another or be commonly formed as a three-way valve. An electrical drive of these valves could be activated by a common control device 34 which also controls or regulates the speed of the drive motor 30. The mixing ratio and thereby the temperature in the feed conduit for the floor heating can therefore be regulated or controlled by way of the control of the valves together with the control of the speed of the drive motor 30. On the one hand a greater range of regulation can be achieved by way of this, and on the other hand losses can be reduced by way of larger valve opening degrees. Hence for example the speed only needs to be briefly increased, in order to admix an increased quantity of heated heat transfer medium.

The invention was described by way of the example of a heating facility. However, it is to be understood that the invention can also be applied in a corresponding manner in other applications, in which two fluid flows are to be mixed. One possible application for example is a system for adjusting the service water temperature as is common in booster pumps for service water supply, in so-called shower booster pumps.

While specific embodiments of the invention have been shown and described in detail to illustrate the application of the principles of the invention, it will be understood that the invention may be embodied otherwise without departing from such principles. 

1. A mixing device comprising: a first inlet; a second inlet; an outlet; a first flow connection; a second flow connection, wherein the first inlet is connected to the outlet via the first flow connection and the second inlet is connected to the outlet via the second flow connection; a circulation pump assembly comprising an electrical drive motor, a control device configured to control a speed the drive motor and impeller arrangement which is driven by the drive motor and is situated in the first flow connection, wherein the flow connections are configured such that at least one hydraulic pressure, which is produced in the first flow connection by the impeller, acts as a hydraulic resistance in the second flow connection.
 2. A mixing device according to claim 1, wherein the first flow connection and the second flow connection unify at a run-out point and the first flow connection and the second flow connection are configured such that the hydraulic resistance acts at the run-out point in the form of a counter-pressure.
 3. A mixing device according to claim 1, wherein the impeller arrangement comprises a first flow path which is part of the first flow connection, and a second flow path which is part of the second flow connection, wherein the flow paths are configured such that a hydraulic pressure which is produced in the first flow path acts as the hydraulic resistance in the second flow path and/or that a hydraulic pressure which is produced in the second flow path (28: 50) acts as the hydraulic resistance in the first flow path.
 4. A mixing device according to claim 1, wherein: the impeller arrangement comprises two impellers which are arranged rotationally fixed to one another and which are commonly driven by the drive motor; and a first flow path which is part of the first flow connection is formed in a first impeller of said two impellers and a second flow path which is part of the second flow connection is formed in a second impeller of said two impellers.
 5. A mixing device according to claim 3, wherein the first flow path and the second flow path are configured to effect pressure developments which are different from one another.
 6. A mixing device according to claim 3, wherein outlet sides of the first and second flow path are spaced different distances from a rotation axis (x) of the impeller arrangement in a radial direction thereof.
 7. A mixing device according to claim 3, wherein: the first flow path in the impeller arrangement runs from a first suction port to an outer periphery of the impeller arrangement; and the second flow path extends from an inlet opening of the impeller to the outer periphery of the impeller arrangement; and the inlet opening is situated radially between the first suction port and the outer periphery of the impeller.
 8. A mixing device according to claim 7, wherein the inlet opening runs out into a flow channel which runs between the first suction port and the outer periphery and which forms at least one section of the first flow path.
 9. A mixing device according to claim 3, wherein: the impeller arrangement comprises a first arrangement of impeller blades, between which first flow channels forming at least a part of the first flow path are situated, and a second arrangement of impeller blades, between which second flow channels forming at least a part of the second flow path are situated; and the first arrangement of impeller blades and the second arrangement of impeller blades are situated in two planes which are offset in the direction of the rotation axis of the impeller.
 10. A mixing device according to claim 9, wherein the first arrangement of impeller blades has a different outer diameter than the second arrangement of impeller blades.
 11. A mixing device according to claim 9, wherein the first arrangement of impeller blades is connected to the first suction port of the impeller arrangement and the second arrangement of impeller blades is connected to a second suction port which annularly surrounds the first suction port or is arranged away from the first suction port.
 12. A mixing device according to claim 1, wherein the control device is configured to vary a speed of the drive motor for regulating a mixing ratio between a fluid flow through the first inlet and a fluid flow through the second inlet by way of changing the hydraulic resistance in at least the second flow connection.
 13. A mixing device according to claim 1, wherein the control device is connected to at least one temperature sensor (36) in the outlet and/or is configured for receiving a signal from at least one external temperature sensor and is configured to vary the speed of the drive motor in dependence on at least one received temperature signal.
 14. A heating system with a mixing device according to claim 1, wherein the first inlet of the mixing device is connected to a return of at least one heating circuit and the second inlet of the mixing device is connected to a feed which comes from a heat source (4).
 15. A heating system according to claim 14, further comprising a second circulation pump assembly arranged in the feed such that the second circulation pump assembly provides a fluid at a preliminary pressure at the second inlet of the mixing device.
 16. A method for temperature-adjustment of a fluid flow of a heating facility, the method comprising the steps of: mixing two differently temperature-adjusted fluid flows in a changeable mixing ratio, wherein the mixing comprises: feeding the two differently temperature-adjusted fluid flows to a common mixing point, at which a hydraulic resistance acts upon at least one of the two fluid flows; and changing the hydraulic resistance by way of a hydraulic means which acts upon at least one of the two fluid flows, for changing the mixing ratio.
 17. A method according to claim 16, wherein the hydraulic resistance is formed by fluid pressure at the mixing point.
 18. A method according to claim 16, wherein the hydraulic resistance is varied by changing fluid pressure of the first and/or the second fluid flow.
 19. A method according to claim 16, wherein a changeable pressure increase is effected in at least one of the two fluid flows by way of a pressure boosting means, wherein the pressure increase is effected by an impeller of a centrifugal pump assembly.
 20. A method according to claim 19, wherein one of the two fluid flows already has a higher preliminary pressure than the other fluid flow before the action of the pressure boosting means. 